The present invention relates to an apparatus for shaping a light beam, having at least two optically functional boundary surfaces that are arranged one behind another in the propagation direction of the light beam to be shaped, such that the light beam can pass through the at least two optically functional boundary surfaces one after another, and two groups of refractive or diffractive imaging elements that are arranged on at least one of the optically functional boundary surfaces.
Apparatuses of the abovenamed type are used, for example, for the purpose of homogenizing laser beams, in particular laser beams of excimer lasers. DE 199 15 000 A1, for example, discloses an apparatus for homogenizing an excimer laser beam that has two lens arrays composed of spherical cylindrical lenses. The lens arrays in this case form two optically functionally boundary surfaces, spaced apart from one another, through which the light beam to be shaped can pass one after another. The cylindrical lenses on the two optically functional boundary surfaces spaced apart from one another are arranged sequentially in this case such that a component beam impinging substantially perpendicularly on the first optically functional boundary surface are switched through a cylindrical lens of the first optically functional boundary surface, and thereupon subsequently passes through a cylindrical lens, aligned with this cylindrical lens, on the second optically functional boundary surface. The component beams passing through the two optically functional boundary surfaces can be superimposed in a processing plane by the positive lens designed as a Fourier lens. It proves to be disadvantageous in this apparatus that the spherical cylindrical lenses are arranged next to one another in such a way as to produce between them a non-defined transition region that either passes or scatters light impinging on it in an uncontrolled fashion. As a result, the intensity distribution of the laser radiation in the processing plane is disadvantageously influenced, and further it is not possible to use the complete area of the optically functional boundary surfaces for shaping the laser beam.
U.S. Pat. No. 6,239,913 B1 discloses an apparatus of the type mentioned at the beginning in which a group of convex cylindrical lenses and a group of concave cylindrical lenses are respectively arranged on two optically functional boundary surfaces. The convex and the concave cylindrical lenses alternate with one another in this case such that the entire boundary surface is covered by the convex and concave lens structures. An apparatus that is possible in accordance with this U.S. patent is to be seen from FIG. 1a, FIG. 1b and FIG. 2a. Cartesian co-ordinate systems are depicted in the figures in order to improve clarity.
FIG. 1a and FIG. 1b show a laser beam 1 that is to be shaped and which moves in the positive Z-direction. The laser beam 1 passes through two lens arrays (2, 3) that in each case have optically functional boundary surfaces 4, 5 on the entrance surface and optically functional boundary surfaces 6, 7 on the exit surface. The laser beam passing through the lens arrays 2, 3 passes through a lens means 8 that serves as a Fourier lens and is designed as a biconvex lens, and is focused thereby in a processing plane 9. Individual component beams of the laser beam 1 are superimposed in the processing plane 9. It may be seen from FIG. 1a and FIG. 1b that the optically functional boundary surfaces 4, 5 on the entrance surface have structures resembling cylindrical lenses and whose axes extend in the X-direction, whereas the optically functional boundary surfaces 6, 7 on the exit surface of the lens arrays 2, 3 have structures resembling cylindrical lenses of which the cylinder axes extend in the Y-direction.
The beam shaping of the laser beam 1 with regard to the X-direction by the optically functional boundary surfaces 6, 7 on the exit surfaces of the lens arrays 2, 3 is to be seen more clearly from FIG. 2a. In particular, only portions of the lens arrays 2, 3 are depicted. It may be gathered from FIG. 2a that the optically functional boundary surfaces 6, 7 on the exit surfaces respectively have alternating convex cylindrical lenses 10, 11 and concave cylindrical lenses 12, 13. It is to be seen with the aid of the component beams 14a, 14b and 15a, 15b, which are drawn in by their example, that component beams 14a, 14b or 15a, 15b impinging at corresponding points on the convex cylindrical lenses 10 of the first lens array 2 leave the convex cylindrical lenses 10 at equal exit angles and pass through the cylindrical lenses 11, respectively aligned with the corresponding convex cylindrical lenses 10, of the second lens array 3. The component beams 14a, 14b or 15a, 15b exiting the convex cylindrical lenses 11 of the second lens array 3 leave these convex cylindrical lenses 11 at equal angles such that they are focused at the same point in the processing plane 9 by the lens means 8 serving as a Fourier lens. This point is clearly visible on the right-hand side in FIG. 2a. Thus, the Fourier lens permits a superimposition of the component beams passing through different convex lenses 10, 11.
The component beams 16a, 16b or 17a, 17b passing through the concave cylindrical lenses 12 of the first lens array 2 prove to be problematical. In the case of the second lens array 3, the component beams 17a or 16b passing through one of the concave lenses 12 pass through different convex cylindrical lenses 11 such that they impinge on the processing plane 9 at different points. However, component beams 17a, 17b impinging on the same points of neighboring concave cylindrical lenses 12 of the first lens array 2 enter the lens array 3 at an equal angle and are superimposed on one another at the same point in the processing plane 9, as may be seen from the right-hand side of FIG. 2a. It may be seen that the component beams 16a, 16b or 17a, 17b passing through the concave cylindrical lenses 12 of the first lens array 2 impinge essentially on the edge of the region in which the laser radiation is mutually superimposed in the processing plane 9. The result of this is an intensity distribution in the processing plane 9 that may be seen from FIG. 2b. In this intensity distribution, there is a middle, comparatively flat, plateau 18 two outer intensity peaks 19 that project upward above the level of the plateau 18. The outer intensity peaks 19 are each adjoined by respectively outwardly dropping edges 20. These outer intensity peaks 19 prove to be extremely disturbing for various applications. It would be particularly desirable to achieve a comparatively uniform intensity distribution, in particular an intensity distribution for which the intensity peaks 19 do not occur.
The problem on which the present invention is based is to create an apparatus of a type mentioned at the beginning that can generate a more effectively applicable intensity distribution in conjunction with a comparatively complete utilization of the optically functional boundary surfaces.